Munich in . In , he was appointed Director of the Institute of Theoretical Physics at the University of Berlin. Planck was awarded the Nobel Prize in Physics in for his quantum theory. Planck also made significant contributions in thermodynamics and other areas of physics.
of electrons ejected does depend upon the brightness of light, the kinetic energy of the ejected electrons does not. For example, red light [ ν = ( . to . ) × Hz] of any brightness (intensity) may shine on a piece of potassium metal for hours but no photoelectrons are ejected.
But, as soon as even a very weak yellow light ( ν = . – . × Hz) shines on the potassium metal, the photoelectric effect is observed. The threshold frequency ( ν ) for potassium metal is .
× Hz. Einstein ( ) was able to explain the photoelectric effect using Planck’s quantum theory of electromagnetic radiation as a starting point. the minimum energy required to eject the electron is h ν (also called work function, W ; Table . ), then the difference in energy ( h ν – h ν ) is transferred as the kinetic energy of the photoelectron.
Following the conservation of energy principle, the kinetic energy of the ejected electron is given by the equation . . ( . ) where m e is the mass of the electron and v is the velocity associated with the ejected electron.
Lastly, a more intense beam of light consists of larger number of photons, consequently the number of electrons ejected is also larger as compared to that in an experiment in which a beam of weaker intensity of light is employed. Dual Behaviour of Electromagnetic Radiation The particle nature of light posed a dilemma for scientists. On the one hand, it could explain the black body radiation and photoelectric effect satisfactorily but on the other hand, it was not consistent with the known wave behaviour of light which could account for the phenomena of interference and diffraction. The only way to resolve the dilemma was to accept the